In recent years, the underground power distribution industry has come to recognize the desireability of employing separable connector arrangements involving complementary, interfitting members, one designated an elbow and supporting a pinshaped male contact element spaced coaxially interiorly of an encircling elastomeric shielded, insulated housing, and the other designated a bushing insert and having an elastomeric shielded, insulated housing including interiorly thereof a female contact element supported coaxially in the bushing housing for receiving the male contact element. In accommodating electrical stresses imposed in use and in permitting entrapment of air without deleterious ionization thereof, such separable connectors have since their inception incorporated structural features such as are shown in commonly-assigned U.S. Ruete et al. Pat. No. 3,243,756 and U.S. Ruete Pat. No. 3,344,391.
Elbows and bushings of the aforementioned type include elements fabricated of materials capable of evolving an arc-quenching gas upon being exposed to an electrical arc struck between the male and female contacts upon joinder and separation thereof. In the elbow, such material is in the form of a pinshaped pin-shaped follower secured to the male contact element forwardly thereof. In the bushing, such material is in the form of a guide supported forwardly of the female contact element for receiving the follower. These well-known features are shown, for example, in commonly-assigned U.S. Brown Pat. No. 3,654,590, which discloses a prescribed axial spacing between the guide and its associated female contact element, such spacing being defined in relation to arc strike distance and being particularly remedial when the elbow and bushing are joined under a fault closure condition.
Some bushings in use presently are constructed with all parts thereof in fixed mutual positional relation, as described, for example, in the commonly-assigned U.S. Pat. to Ruete et al. No. 3,539,972. Recently, however, the industry has seen the development of bushings in which parts are movably supported and are responsive to arc-generated gas pressures in the bushing to be displaced in a manner intended to accelerate the engagement of conductive members to extinguish any arcs struck therebetween. In one such moving part bushing, as disclosed, for example, in U.S. Kotski Pat. No. 3,542,986, the female contact element is supported for axial movement by a piston against the head of which arc-generated gas is applied. Thus, a piston assembly is disposed for unitary movement in the bushing and includes such piston and female contact element and an insulative sleeve encircling the female contact element and supporting the aforementioned guide. Whereas electrical continuity from the female contact element to the exteriorly accessible bushing terminal, is attained in the fixed part bushing simply by fixedly connecting the female contact element to the bushing terminal, the Kotski-type of moving part bushing employs a flexible electrical cable connected at one end thereof to the piston (which is in turn electrically connected to the female contact element) and at its other end to the bushing terminal.
In another version of moving part bushing, described in Joy Manufacturing Company Bulletin 215-4, January 1972, the bushing terminal fixedly supports the bushing female contact element, as in the fixed part bushings. A piston assembly encircles the female contact element and is axially movable thereon. The piston assembly supports and is electrically connected to a so-called arcing ring which is disposed forwardly of the female contact element so as to be disposed to engage the male contact element in the course of its travel to the female contact element. Valve means tightly encircling the female contact element rearwardly of the piston assembly is opened by arc-generated gas evolved under fault closure conditions and the gas displaces the piston assembly and hence the arcing ring to accelerate engagement thereof with the male contact element to extinguish an arc struck therebetween.
In a third type of moving part bushing, set forth in copending commonly-assigned application Ser. No. 406,281, filed on Oct. 15, 1973 on behalf of applicants herein, the first-mentioned type of moving part bushing is modified by introduction therein of a valve member transversely of the bore of the piston supporting the movable female contact element and the further introduction of a spring member exerting rearward axial force on the piston assembly and compressible upon forward piston assembly movement. The spring member serves to enhance rapid separation of the contact elements upon withdrawal of the male contact element from the bushing. Thus, upon separation of the male contact element from frictional engagement with the guide and female contact element, the piston assembly is spring-driven rearwardly of the forwardly exiting male contact element to quickly stretch and therefore aid in extinguishing the arc struck therebetween.
With respect to both functional capability and structural simplicity, the first- and third-mentioned types of moving part bushings are superior to the second-mentioned type. In this regard, the Joy piston assembly defines lesser piston head area than the Kotski piston head, since the former can be of no greater expanse than the limited annular space between its female contact element and the housing. Further, the reliance of the Joy arrangement on sliding engagement of the piston assembly on the female contact element for electrical continuity is less desirable than the substantially constant electrical continuity provided by the flexible cable of the Kotski-type bushing.
Despite the apparent solution to fault closure bushing problems in the fixed part bushing and in the Kotski-type moving part bushing, both bushings have disadvantages. The fixed part bushing is clearly not favored where it is desired to render fault closure somewhat independent of operator performance, as is provided by the moving part bushing. On the other hand, as mentioned above, the Kotski-type moving part bushing requires the flexible cable which acts undesirably as a baffle in a pressure conduit, occupies bushing axial extent otherwise usable for increasing piston stroke, is exposed to the destructive action of arcing and may become self-entangled, impeding piston movement. Furthermore, in manufacture, the flexible cable requires two joinder steps, one end to the piston and the other end to the bushing terminal, and such steps require considerable care in practice.